While working with data most of the time we have to work with relation between different lists of data. Many a times we want to fetch data from both the list at once. This requires us to make different kind of joins between the lists of data.
LINQ support different kinds of join
Inner Join
List<Customer> customers = GetCustomerList();
List<Supplier> suppliers = GetSupplierList();
var custSupJoin =
from sup in suppliers
join cust in customers on sup.Country equals cust.Country
select new { Country = sup.Country, SupplierName = sup.SupplierName, CustomerName = cust.CompanyName };
Group Join – where By the joined dataset is also grouped.
List<Customer> customers = GetCustomerList();
List<Supplier> suppliers = GetSupplierList();
var custSupQuery =
from sup in suppliers
join cust in customers on sup.Country equals cust.Country into cs
select new { Key = sup.Country, Items = cs };
We can also work with the Left outer join in LINQ like this.
List<Customer> customers = GetCustomerList();
List<Supplier> suppliers = GetSupplierList();
var supplierCusts =
from sup in suppliers
join cust in customers on sup.Country equals cust.Country into cs
from c in cs.DefaultIfEmpty() // DefaultIfEmpty preserves left-hand elements that have no matches on the right side
orderby sup.SupplierName
select new { Country = sup.Country, CompanyName = c == null ? "(No customers)" : c.CompanyName,
SupplierName = sup.SupplierName};
Vikram